That day, Mitt Romney’s campaign spent $2,851 buying the rights to various domain names at GoDaddy.com, the vendor that sold the Perry domains.

You might assume it was Romney’s team that scooped up the anti-Perry Web addresses with hopes of launching sites attacking Romney’s chief rival for the 2012 Republican presidential nomination.

Not so, says the Romney campaign.

Such is the latest mystery of Campaign 2012.

The mystery is tough to unravel, because whoever bought the addresses hid his or her identity behind Domains by Proxy, a third-party company frequently used to shield the owners of Web addresses.

The same company was used to register mittromney.com. But a Romney spokesman said that the campaign does not own the Perry domains in question. The campaign would not say which domains it bought Sept. 2.

The recent transactions open a window onto the often secretive online underworld of presidential politics. Along with knocking on doors and airing television spots, campaigns try to blanket their messages — pro and con — across the Internet, which has a whole set of rules and tricks.

A Washington Post analysis of federal campaign spending reports shows that President Obama and Romney spent thousandsof dollars this summer at Go­Daddy.com.

The Perry campaign said it had not bought many domains; it reported no such expenditures in its campaign finance report filed last week.

“The public is more interested in how the candidates can create jobs and improve the economy, not how many domain names you can rack up,” Perry spokesman Mark Miner said. “We’re not running for student body council here. This is for president of the United States.”

But Perry’s opponents and other parties are buying up domains about Perry. In most cases, the addresses have not been put to use and lead to empty Web pages.

In several instances, anti-Perry domains were bought on the same dates that the Romney or Obama campaigns reported making transactions at GoDaddy.com, according to an analysis of online domain-registration records.

On Aug. 15, two days after Perry launched his campaign, Obama’s campaign spent $3,958 at Go­Daddy.com. At least 70 domains containing Perry’s name were bought on the same date.

Among the domain names that were registered anonymously: americansagainstperry.com, christians4rickperry.com,christiansagainstperry.com, evangelicals4perry.com and therealrickperry.net.

It is unknown which domains, if any, were bought by the Obama campaign. Some might have been snatched up by squatters who buy domain names at a cut rate with hopes of selling them for a profit.

Obama spokesman Ben LaBolt said the campaign did not buy any of the Perry addresses in question.

The Obama campaign is the registered owner of at least 355 domains, most of them promoting Obama and his campaigns in key states, according to an analysis by DomainTools, a company that collects data on Web addresses. Only three of the names pertainto a current GOP candidate:mittquiz.com, mittquiz.net and mittquiz.org. The inventory does not include domains that may have been purchased anonymously through Domain by Proxy or other third-party companies.

The Obama campaign is operating several separate Web sites, including attackwatch.com, which provides what the campaign calls “the truth” against “unfounded attacks.”

“These sites are a key part of our strategy to talk directly to voters,” said Teddy Goff, the Obama campaign’s digital director.

TV ad campaigns cost millions of dollars, but domains are cheap. At GoDaddy.com, a new dot-com address costs $11.99 for each year of ownership — less if bought in bulk.

Buying up domains is hardly a new political tactic. In 2004, Democrat Howard Dean pioneered it at the presidential level. But Obama and Romney have taken the practice to new heights.

“It’s just smart,” said J.P. Freire, a senior communications strategist at New Media Strategies. “It’s like due diligence.”

“I wouldn’t make a rush to judgment that everything you’re purchasing when it comes to godaddy is about other campaigns,” Moffatt said. adding: “You try to think through the domains that you would want to have and make sure that you control those assets.”

Moffatt would not say which Web addresses the campaign has bought but said that many of them are positive in nature, such as those promoting a campaign initiative or relating to the campaign in a particular state.

Other sites are connected to a message the campaign is trying to drive. The Romney campaign maintains obamaisntworking.com, a Web site that promotes the “Obama Isn’t Working” theme and includes a countdown clock to November 2012.

Romney’s campaign reported spending $398 for two subscriptions to DomainTools, which offers the ability to monitor domains as other parties buy them, among other services.

“If you don’t have an online strategy and are not thinking constantly about what domains you want people to have the possibility to go to or just block, then you’re not thinking on all cylinders,” said Joe Trippi, a veteran Democratic strategist who ran Dean’s campaign.

In many ways, this is a natural extension of corporate marketing trends. Businesses sometimes boast dozens of microsites on specific products or messages.

“Domains are really 21st-century real estate,” said Warren Adelman, president of GoDaddy.com. “The sophistication that we’re seeing in business around integrated online marketing is now happening in the political world as well.”